The present invention relates to a microscope comprising a main objective having a variable focal length and comprising an illuminating unit including a light source and an illuminating optical system for generating an illuminating beam path directed onto an object plane and extending outside the main objective, means being provided for centering the illumination dependent on a variation of the focal length of the main objective.
Microscopes of this type are known from DE 195 23 712 C2 and DE 195 37 868 B4. In the first-mentioned DE 195 23 712 C2 a stereomicroscope comprising a main objective with variable focal length, a downstream zoom system and a binocular tube as well as an illuminating unit arranged adjacent to the main objective is disclosed. The main objective comprises a fixed and a movable lens for varying the focal length and the intercept length of the main objective. The fixed, negative lens of the main objective is arranged towards the object plane, the movable, positive lens is arranged behind it (facing away from the object plane). A movement of the movable lens in the direction away from the object plane results in a reduction of the focal length of the main objective. For an optimal illumination of the (shifted) object plane, it is suggested in this document to adjust the position of an illumination deflector element dependent on a focal length variation of the main objective for centering the illumination. This is done in that the prism lens used as an illumination deflector element is pivoted such that the illuminating beam path tracks the changed object position. For this purpose, the prism lens is pivotally mounted about an axis which is perpendicular to a plane that is spanned by the vertical optical axis of the main objective and the illuminating beam path which is incident substantially horizontally inclined on the prism lens. As a result thereof, for all positions of the movable lens of the main objective facing away from the object a focusing of the illuminating light on the respective focal point of the main objective can be guaranteed.
The coupling of the rotary movement of the illumination deflector element with the linear (vertical) movement of the lens of the main objective facing away from the object, as suggested in this document, requires very sensitive rotary movements of the illumination deflector element in relation to the movement of the lens and makes high demands on the mechanical coupling which is designed with a high constructional expense in this document. Any disturbances will be directly visible for the user (particularly given high magnifications). Further, the size of the surface of the deflector element turns out to be disadvantageous, as it has to be sufficiently large in order to cover the entire illuminating pencil even when the illumination deflector element is tilted. As illumination deflector elements, mirrors or the mentioned prism lenses can be used. When mirrors are used, an increase of the reflecting surface will result in the additional disadvantage of an increased required thickness of the reflecting surface. Thus, altogether the required space and the height of the weight to be moved are increased.
In the mentioned DE 195 37 868 B4, an illuminating device for a stereomicroscope comprising an objective with a variable image-forming intercept length is disclosed, an illumination intercept length variation being possible via an optical system that is separate from the viewing optical system. Means for coupling the intercept lengths mentioned are disclosed, which means effect that the illumination intercept length and the image-forming intercept length correspond to one another. Further, means for coupling are provided which guarantee that the angular position of a deflector element of the illuminating device is varied such dependent on the respective image-forming intercept length and illumination intercept length that there is always a centered illumination of the viewed field of view. Since, here too, for centering the illumination, rotary movements of the illumination deflector elements are performed, here, once again, the disadvantages mentioned occur.
A basically different possibility of illumination centering results when the illumination is guided through the main objective of the microscope. This solution is implemented in the surgical microscope models M520 and M525 of the applicant. Here, the illumination deflector element directs the illuminating beam path to and through the main objective having variable focal length so that the illumination is always centered on the focus.
An optical binocular viewing system comprising one main objective common for both channels and a viewing zoom system as well as an illuminating system having an illuminating zoom system is suggested in EP 0 321 586 B2. The illuminating beam path is guided through the main objective via a deflecting prism. The illuminating zoom system is adjusted dependent on the viewing zoom system in order to adapt the size of the illuminated field to the varying zoom magnification.
The microscopes mentioned up to now use vertical zoom systems, i.e. the longitudinal axis of the zoom system lies parallel to the optical axis of the main objective. If, in addition, the illumination is fed into the main objective from above, there will be a high space requirement in vertical direction resulting in microscopes having a relative high overall height in the vertical direction. This is disadvantageous for ergonomic reasons since the distance between the eyepiece and the main objective is increased.
From U.S. Pat. No. 6,473,229 B2, a stereomicroscope comprising a horizontally arranged illuminating unit is known, the illuminating beam path of which being directed via a fixed deflecting mirror outside the main objective onto the object plane. The stereomicroscope suggested therein has a main beam path and an assistant beam path, for each of the two beam paths separate optical systems comprising a lens system, a zoom system and a binocular tube being provided. While one of the zoom systems is designed such that is lies horizontally, the axis of the other zoom system is inclined to the vertical which is perpendicular to the object plane. Here, with respect to illumination centering given a variable focal length of one of the lens systems no suggestions are made.
For reducing the vertical constructional height, a stereomicroscope structure has been suggested in EP 1 424 582 B1, in which a “lying” zoom system, i.e. a zoom system having its longitudinal axis arranged horizontally, is realized. For this purpose, there is arranged between the main objective and the zoom system a deflector element which deflects the viewing beam path from a substantially vertical direction into a substantially horizontal direction and feeds the same to the zoom system arranged in a first horizontal plane. By means of further deflector elements the viewing beam path exiting the zoom system is deflected into a second horizontal plane which extends substantially parallel to the first horizontal plane and in which optical add-on components are arranged. With respect to details on the structure and the mode of functioning of such a stereomicroscope with “lying” zoom system reference is explicitly made to the mentioned European patent specification.
In this stereomicroscope, the illuminating unit is arranged substantially adjacent to the main objective in horizontal direction und below the zoom system in vertical direction, the illuminating beam path being guided outside the main objective. Instead of an illumination centering, it can be ensured by means of a sufficiently large illuminated field that the visual field is always illuminated given a focal length variation of the main objective. Such a generously designed illuminated field requires a correspondingly largely designed illuminating unit which in turn has a negative effect on the ergonomics of the microscope. A further disadvantage is here that the homogeneity of the illumination (distribution of the illuminated field) cannot be the same for all positions of the multi-focus (variable focus lens). Only another part of the entire available illuminated field is used.
Finally from DE 101 44 062 A1 and the corresponding U.S. Pat. No. 7,102,818 B2 a stereomicroscope comprising an illuminating device is known, in which the illuminating beam path is faded into the main beam path of the microscope from a substantially horizontal direction via a deflecting mirror and is guided to the object via the main objective. The diameter of the deflecting mirror is here larger than the distance between the viewing beam paths (stereobasis) and it has free openings for the viewing beam paths. In addition, in the illuminating device suggested therein, a diaphragm is provided which can be radially shifted in the illuminating beam path, as a result whereof the angles of incidence of the light beams illuminating the object can be varied in radial direction (relative to the main beam path of the microscope). In this way, the object can be illuminated from various angles without the illuminated field being shifted laterally. Since the illuminating beam path is guided through the main objective in this document, the problems relating to the illumination centering is naturally not mentioned therein. A large illuminating aperture is required for the way of proceeding suggested herein (which, in practice is often not sufficiently present).
In addition, a tracking of the illuminated field with respect to position and size has the advantage that the diameter of the illuminated field can be kept at a minimum and be adapted to the field of view so that in the case of surgical microscopes the patient will be exposed to a minimum of radiation.
The present invention is to be particularly suitable for the illumination centering in a microscope structure making use of “lying” zoom systems.